Telecine or film scanning equipment used to produce such signals from cinematographic film have been known for many years, and are described for example in “TV and Video Engineers Reference Book” Chapter 39 Butterworth and Heinemann ISBN 0-7506-1021-2. There are two main types of film scanner: diffuse light illumination, and spot scanning. The former uses a diffuse light source to illuminate a frame of film and optics to image the illuminated frame on to a light detector, such as a line array or area array CCD detector. Spot scanning systems use a flying spot of light to successively illuminate points of film. Light transmitted by the film is collected by light collection optics and converted to electrical signals by a detector.
Known telecines or film scanners that uses a scanning “spot” light source include the known Ursa™ or C-Reality™ telecines of Cintel International Limited. The illumination and light collection systems of the C-Reality™ telecine comprises a Cathode Ray Tube (CRT) which produces a raster scan that is imaged onto the film by an imaging lens group. Light passing through the film is modulated by the colour and density of the film at each location or pixel scanned, this light being subsequently analysed into its red, green, and blue components. Lenses then collect the light from the film and apply it to the Avalanche Photo Diode sensors. A dichroic mirror separates the received light into blue, red and green components. The three electrical colour signals are then passed through electronic processing circuits, converted into a television signal format on digital data and provided as output signals.
A known system of the type using spot scanning, described in GB-B-2,370,439, collects light that is scattered by scratches on the surface of, or other deformities in or on, the film. Such scratches cause scattering of the light, which would then be lost from the optical system that collects the light and cause a reduction in the signal received by the photo sensors. By collecting this light the visibility of the scratches in the resultant electrical images is much reduced.
The ray collection of this known system uses an integrating sphere or cylinder to collect all light from film (both scratched and unscratched areas). This method collects substantially all angles of light rays from the film. The light collection system when disposed in a film scanner has the advantage that light transmitted by film and imaged onto one or more image light sensors is transmitted in the usual manner, whereas light scattered by scratches is collected within the internally reflecting cavity and detected by the scratch light sensor. The signal produced by the scattered light sensor can be used to compensate the signal produced by the image light sensors to reduce the visibility of a scratch or other defect causing scattering.
We have appreciated, though, that such light collection techniques cannot work with diffuse illumination scanners such as CCD array scanners. This is because the film, in CCD scanners, is illuminated with diffuse light and imaged by an optical system onto a CCD array. This imaging process requires that the CCD array is at an image focus of the film so that each portion of the film is imaged uniquely onto the CCD array. Accordingly, techniques such as using integrating spheres to capture light from film cannot be used.